Add Manual and Python Reference Links for Custom Operators
There are two functions that takes you to the docs:

# Blender docs
bpy.ops.wm.doc_view_manual(doc_id="")

# Blender Python docs
bpy.ops.wm.doc_view(doc_id="")


It seems that they take their parameters from the property as follows:

doc_id = data.identifier + property_name


where the property has been created in this manner:

col.row().prop(data, property_name)


Those functions search the _manual_map for this doc_id. The manual_map contains by default the blender_default_map which is (prefix, manual_mapping ).

The prefix is simply 'https://blender.org/manual' while manual_mapping is dict you give it the something+doc_id (in this case bpy.ops) and you get the rest of the url (url = prefix + manual_mapping[doc_id])

So to add you manual you create your addon_map:

import bpy

prefix = "https://myaddon.org/manual/"
my_manual_mapping =(
    ("bpy.ops.myaddon.*", "page_one"),
    ("bpy.ops.myaddon.something.*", "page_one/page_two.html")
)

def my_map():

  ret = (prefix, my_manual_mapping)
  return ret

bpy.utils.register_manual_map(my_map)


bpy.ops.wm.doc_view_manual(doc_id="") will now take you to your site.

(Note: I have this in my addon: bl_idname = "myaddon.simple_operator")